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Discussion Starter · #1 ·
while driving my car I noticed that the temp constantly fluxuates between the middle and just before the red. it will stay just before the red 3 or 4 seconds then slowly drop anywhere to 3/4 and mid temp slowly then back up. it constantly does this as though there are 2 temp controlling functions. one to keep the car in the middle range which isn't functioning and one that keeps it from overheating which is working. I haven't been able to determine if the fan kicks on just before over heating or anything like that. it does it regardless if I'm sitting still or cruising at 60. also worth noting. I recently did a coolant overhaul. new stainless Stewart pump, new radiator, expansion tank, thermostat, hoses etc.99 323i standard shift.
 

· Keeping it surreal
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43,843 Posts
Sometimes you get a stubborn air bubble trapped in the system that will cause this. Try bleeding it again, with the front end raised up a little, and the heater set to full on with the fan going.
 

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The easiest way is to run your car up on some ramps, to get the front elevated, as FastBob mentioned. Be careful that the ramps don't hit the wrap-around portion of your front end, before having the tire roll up on it first. With my ZHP, I have to place a 3 foot 2x8 board inclined on the ramp to get it raising early before it gets to the ramp.

Use the bleeder screw and take your time. You'll get the bubble out that way.
 

· BMW driver/rider
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194 Posts
Has it been doing it since the overhaul?

I'd try going into the hidden OBC functions and monitoring the temp there and see if it fluctuates like the gauge does. Number 7.0 in the list. You can access the functions just with the key on and then start the car and drive it and it will stay on that function readout until you turn the ignition off.

Instructions to access the hidden OBC functions:
1. Hold Trip Reset while turning ignition key to on position
2. OBC should show "Test"
3. Repeatedly press Trip Reset to select function 19.0 to unlock all of the features
3. Wait for display to show "Off"
4. Depress Trip Reset for 1/4 second and release it
5. With no delay press Trip Reset several times to select one of the following functions:

Example description
1 Car Engine and cluster data
1.0 46nnn Chassis nr/VIN serial number (last 5 digits)
1.1 4nnn K-number
1.2 690236 Cluster Part #
1.3 045210 Coding (04)/diagnosis (52)/bus index (10)
1.4 1200 Week (12)/year of manufacture (2000)
1.5 09_160 Hardware (09) and software # (16.0) of cluster
1.6 Not used
1.7 04__44 CAN-version (04) KI-revision index (44)
2 (test) Cluster System Test - Activates the gauge drivers,
indicators and LEDs to confirm function
3 SI Data
3.0 1098 Used fuel in liters since last SI (Service Inspection)
3.1 0231 Periodic inspection days; elapsed days (since last SI)
4 Momentary Consumption
4.0 0145+ Instant fuel consumption - 0145=14.5 liters/100km
4.1 0018 Instant fuel consumption - 0018=1.8 l/Hour
5 Distance Gone Consumption
5.0 082 Average mileage; 082=8.2 liters/100km
5.1 0536 Calc. km to refuel (momentary distance to go)
6 Fuel Level sensor inputs in liters
6.0 109330+ Fuel level averaged; Left half sensor input=10.9 liters; Right sensor input=33.0 liters
6.1 0439+ Total tank level averaged; vlgs 6.0: 10.9+33.0=43.9 liters
6.2 0442+ Indicated value (44.2) and tank phase
7 Temperature and Speed
7.0 021+ Coolant/Engine temperature (2.1C)
7.1 130 Ambient/Outside temperature - chg met 5 pts. 125/130/135
7.2 + Engine speed / Current RPMs 1/min
7.3 + Vehicle speed / Current Speed in km/hour
8 Input value in HEX form
8.0 1d0+ System voltage ADC-Value Hex code
8.1 26C33C+ ADC Values HG left/HG right
8.2 0000 ADC Value brake degradation sensor (000=o.k.)
8.3 18C ADC Value outside temperature
9 Battery
9.0 140 Battery Voltage - 140 = UB 14.0v
9.1 242013+?
9.2 074_78+?
9.3 0011+?
10 Not used
11 Not used
12 Not used
13 GonG Gong Test
14 Not used
15 Status cluster I/O-ports (bit codes) 0=low; 1=high
1st-belt contact, seat belt fastened=0; 2) ignition lock contact, key inserted=0; 3) door contact, door open=0; 4) clock button pressed=0; 5) SI reset=0, for reset=0; 6) EGS transmission failure=0
Status Digital Outputs (bits) 0=inactive, 1=active
1) Gong output; 2) Brake warning lamp; 3) Low fuel warning lamp; 4) EGA lamp; 5) seat belt lamp; 6) manipulation dot
16 Not used
17 Not used
18 Not used
19 Lock Status; unlocks functions in range 3-18
19.0 L-On/L-Off Unlock: press button when "L-Off"
20 Not used
21 Software Reset; reset OBC settings
00 End of test
 

· Keeping it surreal
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43,843 Posts
thanks. will try. note. I do have about 6000 miles since coolant overhaul
After reading this, and re-reading your original post, I would lean toward a faulty thermo-sensor....when operating "normally", they are buffered, so the needle`s movement is rather sluggish, not reacting quickly as you describe.
 

· ROLL TIDE!
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· Registered
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Discussion Starter · #12 ·
so I tried the bidden diagnostic. check. both temps match or at least change at the same rate. I'm tryin to do the ramp bleed with the cap since I have to jerry rig the vent shut now till my new plug comes.
 

· Keeping it surreal
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43,843 Posts
when the heat is on the temp stays steady like it should. what does this tell me? still air?
The heater is acting as a liquid-to-air intercooler, bleeding excess heat out of your cooling system....the cause of the problem could be any one of a number of things, air bubble, failing water pump, bad fan, clogged radiator, partially-stuck T-stat, etc.
 

· ROLL TIDE!
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24,184 Posts
The heater is acting as a liquid-to-air intercooler, bleeding excess heat out of your cooling system....the cause of the problem could be any one of a number of things, air bubble, failing water pump, bad fan, clogged radiator, partially-stuck T-stat, etc.
Having had 3 bad tstats on my last car, I'd say replace it again and see what happens.
 

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Discussion Starter · #16 ·
that makes sense to me. if the heater core seeing such a small amount of airflow helps so much and not 60+ MPH wind over the radiator it would seem that the thermostat is closed and the outside air is uneffecting the actual temp. great. I start work 2.5 hrs away in center city philly traffic tomorrow.
 

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Discussion Starter · #17 ·
now this.morning the temperature on the hidden diagnostic went up to 235 while the temperature guage in the car showed temp in the middle.. any ideas? with no signs of overheating. that was just before I arrived on my long ride. the rest of the drive both temps changed equal to one another. I'm going to put in my old thermostat after work to see if it helps after work since it was working fine and ill have to special order a new.one anyway.
 
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